CS170 Discussion – 2009-05-01

1. CS170 Discussion – 2009-05-01 Bryce Boe

2. 9 Days left… • of your favorite class ever • of the best time of you life • of the most you’ve ever worked in your life • to complete project 6 • with the coolest TA ever (jk – or am I?)

3. Project 6 – Immediate Files

4. Why? Mullender, S. J. and Tanenbaum, A. S. 1984. Immediate files. Softw. Pract. Exper. 14, 4 (Jun. 1984), 365-368. DOI= http://dx.doi.org/10.1002/spe.4380140407

5. Inside Minix

6. v1, v2, v3 files • v1 files are for older files -- ignore • v2 files are what this version of minix creates • v3 files don’t exist, however there are a few comments about them -- ignore

7. servers/mfs/inode.h EXTERN structinode { mode_ti_mode; /* file type, protection, etc. */ nlink_ti_nlinks; /* how many links to this file */ uid_ti_uid; /* user id of the file's owner */ gid_ti_gid; /* group number */ off_ti_size; /* current file size in bytes */ time_ti_atime; /* time of last access (V2 only) */ time_ti_mtime; /* when file data last changed */ time_ti_ctime; /* when was inode itself changed */ zone_t i_zone[V2_NR_TZONES]; /* zone numbers */ … <remainder of struct not saved on disk> }

8. include/minix/const.h • Defines constants used by mfs • I_REGULAR – regular file • I_TYPE – mask for file type • Note: These are used in ushorts (2 bytes) • Suggestion: Add an I_IMMEDIATE that fits in ushort and doesn’t conflict with the masks

9. Constants • I_TYPE 0170000 /* inode type */ • I_SYMBOLIC_LINK 0120000 /* symbolic link */ • I_REGULAR 0100000 /* regular file */ • #define I_BLOCK_SPECIAL 0060000 /* block special file */ • #define I_DIRECTORY 0040000 /* file is a directory */ • #define I_CHAR_SPECIAL 0020000 /* character special file */ • #define I_NAMED_PIPE 0010000 /* named pipe (FIFO) */ • #define I_SET_UID_BIT 0004000 /* set effective uid_t */ • #define I_SET_GID_BIT 0002000 /* set effective gid_t */ • #define ALL_MODES 0006777 /* all bits for u,g,o */ • #define RWX_MODES 0000777 /* mode bits for RWX only */ • #define R_BIT 0000004 /* Rwx protection bit */ • #define W_BIT 0000002 /* rWx protection bit */ • #define X_BIT 0000001 /* rwX protection bit */ • #define I_NOT_ALLOC 0000000 /* this inode is free */

10. Adding Files • Set immediate flag whenever a regular file is initially created • Suggestion: Trace all the places where files can be created back to common code. • Hint: Somewhere in servers/mfs/open.c

11. Deleting Files • When files are deleted typically indirect blocks need to be freed • Skip this step if immediate • Suggestion: As before trace the few places that perform this behavior to the common location • Hint: servers/vfs/link.c

12. Writing Files • When file size grows beyond 34 bytes switch to “normal” method

13. Reading Files • If immediate read from inode • If not read as normal

14. How to start • Step 1: Successfully set immediate bit, and put checks on open/read/write/delete when an immediate file is encountered. • Step 2: Implement the immediate file • Warning: Make regular backups of your minix image, as you might destroy it